feat: inline some mentions to reduce spacing

[patak-dev]

Description

After #1293 (and 5785047), if you add a new mention in a conversation, a mention-group will be created only with it as the others are removed from the context. This could break the context, especially now that we edit with the grouped mentions so people may start using the initial handle as part of the text. But the main issue to me is that a mention-group that only has one or two handles ends up occupying more space extracted than inlined.

This PR lets mentions be inlined when only 1 or 2 remain to be shown and creates a mention-group when there are 3 or more.

Elk 0.5.0

Elk before this PR

After this PR

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